Harmful Algal Blooms in the Midwest: What They Are and How USGS Tracks Them

Algae are the base of the aquatic food web and make oxygen that other living things breathe. In the right amounts they support a healthy, diverse ecosystem. But when they grow explosively, the result — a harmful algal bloom, or HAB — can poison people, pets and wildlife, suffocate fish and shut down swimming, boating and fishing. The U.S. Geological Survey's Central Midwest Water Science Center, which covers Illinois, Iowa and Missouri, has a team working to predict when blooms will happen, how big they will be and how toxic.

A visible algal bloom in the Illinois River at Henry, Illinois. Credit: Jessica Garrett, U.S. Geological Survey.

What a bloom is

An algal bloom is a rapid increase in algae — aquatic organisms that contain chlorophyll, mostly need sunlight and have no true leaves or flowers. They range from single microscopic cells to seaweed and giant kelp. Most blooms are made of one of two groups:

The cyanobacterium Microcystis aeruginosa*, magnified. Credit: U.S. Geological Survey.*

Blooms are usually blamed on excess nutrients and warm water, ideal conditions for algae. But lakes low in nutrients bloom too, and much less is known about what triggers those. The conditions are complex and often specific to a site.

Why blooms are harmful

• Oxygen crashes. When the algae die, microbes decompose them, using up oxygen. Dissolved oxygen can fall below the levels most living things need, often killing fish.
• Toxins. Some cyanobacteria make toxins that can reach people through drinking water, recreational water and fish, causing skin rashes, fever-like symptoms and respiratory and gastrointestinal problems. Some species make several toxins, and toxins can build up in organisms and move up the food chain.
• Bad taste and smell. Cyanobacteria also make compounds, harmless as far as is known, that make drinking water and fish taste and smell bad; water suppliers pay extra to remove them.
• Lost recreation. The U.S. Environmental Protection Agency discourages water recreation during blooms because of possible toxicity. One study found a 10–13 percent drop in Lake Erie fishing license sales between 2011 and 2014, a period of algal blooms, and many river and lake towns depend on seasonal tourism.
• Less diversity. Blooms can change aquatic communities and lower species richness.

The cost

A 2002 study by Hoagland and others estimated that in the United States HABs cost about $20 million a year in public health effects (from shellfish and ciguatera fish poisoning), $18 million a year on average to commercial fisheries, $7 million a year to recreation and tourism, and $2 million a year for monitoring and management. With blooms becoming more common, those numbers are expected to rise, but no newer estimates have been made because the data vary so much.

What the team is doing

As of 2020 the center had several HAB projects:

• The Illinois River. The Illinois River Basin was chosen as the third basin in USGS's Next Generation Water Observing System, with funding to study blooms there using new technologies. Urban and agricultural effects on water quality make the basin prone to blooms, which are becoming more common. Scientists combine large sampling efforts, continuous real-time sensors and satellite imagery.
• A model of the upper Illinois River. With the Illinois Environmental Protection Agency, USGS is building a model of a bloom-prone stretch, fed by real-time water-quality monitors, streamgages and weather data such as wind speed, air temperature and solar radiation, to understand how water movement and weather drive blooms.
• Mozingo Lake, Missouri. With the Missouri Department of Natural Resources, USGS is developing a monitoring plan for the reservoir, a big recreation area and the drinking-water source for Maryville, where blooms have caused taste and odor problems and lost recreation. A streamgage with continuous water-quality sensors is planned on Mozingo Creek, the main inflow; with nutrient and sediment samples, it can show what is feeding the blooms and support practices to reduce them.

A USGS scientist checks a streamgage at Starved Rock Lock and Dam, Ottawa, Illinois. Credit: U.S. Geological Survey.

Sources

Based on "Central Midwest Water Science Center—Harmful Algal Blooms Team," U.S. Geological Survey Fact Sheet 2022–3011; a work of the United States government in the public domain. It cites Hoagland and others (2002), Anderson and others (2000), Wolf and others (2017), Merel and others (2013) and the U.S. Environmental Protection Agency (2021).